1. Field of the Invention
The present invention relates to a method of managing downlink discontinuous reception for a wireless communications system and related communications device, and more particularly to a method of managing downlink discontinuous reception corresponding to a radio resource control procedure for a user equipment of a wireless communications system and related communications device.
2. Description of the Prior Art
The third generation (3G) mobile telecommunications system, the Universal Mobile Telecommunications System (UMTS), has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of quality of service (QoS) requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. Through the 3G mobile telecommunications system, a user can utilize a wireless communications device, such as a mobile phone, to realize real-time video communications, conference calls, real-time games, online music broadcasts, and email sending/receiving. However, these functions rely on fast, instantaneous transmission. Thus, targeting the third generation mobile telecommunication technology, the prior art provides High Speed Package Access (HSPA) technology, which includes High Speed Downlink Package Access (HSDPA) and High Speed Uplink Package Access (HSUPA), to increase bandwidth utility rate and package data processing efficiency to improve the uplink/downlink transmission rate.
According to the related protocol specifications of the 3rd Generation Partnership Project (3GPP), the Radio Resource Control (RRC) layer, a Layer 3 protocol, is the core of communications protocols related to AS and is located in radio network controllers (RNC) of the UMTS Terrestrial Radio Access Network (UTRAN) and a user equipment (UE). The RRC layer uses RRC messages formed from many Information Elements (IEs) to perform RRC procedures. The RRC layer defines various RRC states to describe the usage of radio resource for the UE. RRC states can be divided into idle mode and RRC connected mode according to whether the RRC connection is established. RRC connected mode are further divided into a CELL_DCH state, a CELL_FACH state, a CELL_PCH state and a URA_PCH state. The UE in the CELL_DCH state uses dedicated radio resources not shared with other UEs, where the UE in the CELL_PCH or URA_PCH state receives paging or broadcasting information from the UTRAN. No data transmission is allowed in the CELL_PCH and URA_PCH states.
The foregoing specification provides downlink discontinuous reception (DL DRX) operation, allowing the UE in the CELL_PCH or the URA_PCH state to receive paging information based on a discontinuous timing mode without burdensome RRC disconnecting, so as to save UE power. The DL DRX operation includes two kinds of reception modes configured with a DRX cycle length coefficient IE and a DRX cycle length coefficient 2 IE, respectively. A UTRAN DRX cycle length coefficient IE includes both of the two IEs and moreover a Time for DRX cycle 2 IE. The two reception modes are hereinafter called first reception mode and second reception mode, respectively. The second reception mode provides better paging efficiency than the first reception mode.
When the DL DRX operation is in use, the UE employs a timer T319 for switching between the first and the second reception mode. In general, when the UE enters the CELL_PCH or the URA_PCH state, using the second reception mode, the UE activates and sets the timer T319 according to the Time for DRX cycle 2 IE. When the timer T319 expires, the UE switches to use the first reception mode. In other words, when the UTRAN does not page the UE for a period longer than the set time of the timer T319, the UE automatically degrades itself to the lower speed paging operation, namely the first reception mode, so as to reduce power consumption.
On the other hand, the UE in the idle mode initiates an RRC connection establishment procedure when attempting to request the UTRAN for an RRC connection. During the RRC connection establishment procedure, the UE sends an RRC Connection Request message to the UTRAN, and the UTRAN correspondingly responds with an RRC Connection Setup message if accepting the request. Finally, the UE sets related parameters or variables according to configuration of the RRC Connection Setup message and then reports back with an RRC Connection Setup Complete message.
The RRC Connection Setup message includes an RRC State Indicator IE indicating an RRC state for the UE to enter and the abovementioned UTRAN DRX cycle length coefficient IE. The UE activates and sets the timer T319 according to the UTRAN DRX cycle length coefficient IE when the indicated RRC state is the CELL_DCH, the CELL_PCH or the URA_PCH state. In this situation, the UE entering the CELL_PCH or the URA_PCH state successfully receives paging information under the second reception mode. However, the abovementioned DL DRX operation is not designed to be applicable for the UE entering the CELL_DCH state. That is to say, the timer T319 is activated in an inappropriate situation, possibly causing system errors in the UE entering the CELL_DCH state.